Highly dispersed and narrowly size-distributed Pt-Co bimetallic nanoparticles supported on CNTs are fabricated by atomic layer deposition (ALD) of Pt followed by COO ALD for hydrolytic dehydrogenation of ammonia borane. The controlled decoration of CoO significantly enhances the hydrogen evolution activity of the Pt-based catalysts due to the remarkable Pt-Co synergy, i.e., the TOF value is up to 675.1 mol(H2)mol(pt)(-1) min(-1) for bimetallic PtCo20/CNTs catalyst, which is 1.8 times higher than that of monometallic Pt/CNTs catalyst. The underlying nature of the Pt-Co synergy is systematically investigated by combining multiple characterizations with kinetic and isotopic analyses. It is revealed that the decoration of CoO onto Pt provides unique Pt-Co interfaces and targeted Pt electronic properties, thereby exhibiting the lower activation energy and favorable O-H bond cleavage being the rate-determining step for the hydrolysis reaction. The insights revealed here provide inspiration and guide for the rational design of other advanced nanocatalysts.